Electrical conductor with polyester insulating layer and method therefor

ABSTRACT

An organic, high-molecular weight polyester containing substantially chain members of the formula ##STR1## wherein X is at least one member selected from the group consisting of ##STR2## having an inherent viscosity of at least 1.0 dl/g, preferably at least 1.2 dl/g measured at 30° C. in a solution of 0.5 g of the polyester in 100 ml of a mixture of 60% by weight of phenol and 40% by weight of 1,1,2,2-tetrachloroethane and whose films cast from a solution in a chlorinated organic solvent have an elongation at break of more than about 20%, preferably at least 40% measured according to ASTM D 882-75 b having excellent properties for electrical insulation as well as other fields.

This is a division of Ser. No. 375,205 filed May 5, 1982 now U.S. Pat.No. 4,388,454.

STATE OF THE ART

U.S. Pat. Nos. 3,216,970 and 3,351,624 of Conix describe the preparationof linear polyesters of aromatic dicarboxylic acids such as terephthaticacid and isophthalic acid and various aromatic diphenols including1,1-bis-(4-hydroxyphenyl)-1-phenyl-ethane but these polyesters have arelatively low molecular weight as evidenced by the low intrinsicviscosity values reported for the polyesters in the patent. It is to benoted that the intrinsic viscosity values reported by Conix would beless if reported as inherent viscosity values used in the presentinvention.

For example, Example 6 of U.S. Pat. No. 3,216,970 reports for thepolyester of 1,1-bis-(4-hydroxyphenyl)-1-phenylethane and isophthaloylchloride an intrinsic viscosity of only 0.7 dl/g and an elongation atbreak of 17% in a different test. Example 11 of the same patent reportsfor the polyester of 1,1-bis-(4-hydroxyphenyl)-1-phenyl-ethane andterephthaloyl chloride an intrinsic viscosity of 0.83 dl/g. Example 3 ofU.S. Pat. No. 3,351,624 is the same as Example 11 of the earlier. Conixpatent. With polyesters of this type, it is not possible to cast filmsor make coatings which have desired mechanical and electrical insulationproperties to be used for electrical insulation.

OBJECTS OF THE INVENTION

It is an object of the invention to provide improved polyesters havingmechanical and electrical insulation properties so they can besuccessfully used in the electrical insulation field.

It is another object of the invention to provide films and powders ofhigh molecular weight polyesters with an inherent viscosity of at least1.0 dl/g and an improved elongation at break.

It is a further object of the invention to provide a novel method ofinsulating an electrical conductor by providing the conductor with acoating of a high molecular weight polyester of the invention.

It is an additional object of the invention to provide an electricalinsulating tape comprising a film of a high molecular weight polyesterof 1,1-bis(4-hydroxyphenyl)-1-phenyl-ethane and isophthalic acid and/orterephthalic acid of the invention having good adhesive properties,especially to metal surfaces.

These and other objects and advantages of the invention will becomeobvious from the following detailed description.

THE INVENTION

The novel polyesters of the invention are organic, high-molecular weightpolyesters containing substantially chain members of the formula##STR3## wherein X is at least one member selected from the groupconsisting of ##STR4## having an inherent viscosity of at least 1.0dl/g, preferably at least 1.2 dl/g measured at 30° C. in a solution of0.5 g of the polyester in 100 ml of a mixture of 60% by weight of phenoland 40% by weight of 1,1,2,2-tetrachloroethane and whose films cast froma solution in a chlorinated organic solvent have an elongation at breakof more than about 20%, preferably at least 40% measured according toASTM D 882-75 b.

The polyesters of the invention have many desirable physical propertieswhich make them valuable for the electrical insulation field. Theseproperties include a high tensile strength, excellent dimensionalproperties, high temperature stability, good flame retardant properties,good adhesion to metals, good electrical insulation properties as seenfrom the dielectric strength and dissipation factors and excellentmechanical properties as well as good water absorption properties.

The novel process for the preparation of the polyesters having aninherent viscosity of at least 1.0 dl/g comprises reacting1,1-bis-(4-hydroxyphenyl)-1-phenyl-ethane or a functional derivativethereof with at least one acid selected from the group consisting ofterephthalic acid and isophthalic acid and functional derivativesthereof in a suitable organic solvent. The functional derivatives of thesaid diphenol may be an alkali metal phenolate such as sodium, potassiumor lithium and the functional acid derivative may be an acid halide. Theprocess is more fully described in commonly assigned U.S. patentapplication Ser. No. 260,939 filed May 6, 1981, now abandoned.

It has been found that it is preferred to use as pure as possible formof 1,1-bis-(4-hydroxyphenyl)-1-phenyl-ethane as indicated by its meltingrange to obtain polyesters with as high an inherent viscosity aspossible. For example, where the said diphenol has a melting range of185° to 190° C. or 188° to 190° C., the resulting polyester with anequimolar mixture of terephthalic and isophthalic acid can result inproducts having an inherent viscosity of 1.65 and 2.11, respectively.

A process for the preparation of phenol-aromatic ketone condensationproducts by reaction of phenols and ketones in the presence of a gaseoushydrogen halide described in copending patent application Ser. No.250,669 filed Apr. 3, 1981, now abandoned, comprises adding in catalyticamounts up to less than molar amounts based on the ketone as anadditional condensation agent at least one bivalent, trivalent ortetravalent metal halide, introducing the gaseous hydrogen halide andafter termination of the condensation reaction, adding water to thereaction mixture and recovering the purified condensation product toform monomers of 9,9-bis-(4-hydroxyphenyl)-fluorene with a melting pointof at least 226° C. and 1,1-bis-(4-hydroxyphenyl)-1-phenylethane with amelting point of at least 189° C. which contain minor residual amountsof metal catalyst.

A preferred mode of the process comprises reacting an aqueous phasecontaining the disodium salt of1,1-bis-(4-hydroxyphenyl)-1-phenyl-ethane with a melting range of atleast 188° to 189° C. with an organic phase containing acid chloride ofat least one acid selected from the group consisting of isophthalic acidand terephthalic acid in a suitable organic solvent in the presence of aphase transfer catalyst such as benzyltriethylammonium chloride ortetrabutylammonium iodide to obtain a polyester with an inherentviscosity of at least 1.0, preferably 1.2 dl/g or higher. The polyestersof terephthalic acid alone tend to have higher inherent viscosities.

The dicarboxylic acids may be used individually or as mixtures,preferably in a ratio of 70 to 30% of terephthalic acid to 30 to 70% byweight of isophthalic acid, and most preferably as an equimolar mixtureof terephthalic acid and isophthalic acid as the elongation at breakvalues are higher.

The polyesters of the invention may be made in the form of thin films,preferably with a thickness of 0.010 to 0.250 mm, preferably 0.020 to0.150 mm by known methods such as forming a solution of the polyester ina suitable organic solvent, forming a film of the solution on a smoothsurface, evaporating the organic solvent and removing the resultingpolyester film.

As noted above, the polyester films of the invention have excellentelectrical insulation properties and more important have excellentmechanical properties as indicated by their elongation at break anddimensional stability. Moreover, the good mechanical properties permitthe production of good quality films without regard to productionrelated fluctuations.

Polyesters based on 1,1-bis-(4-hydroxyphenyl)-1-phenylethane andisophthalic and/or terephthalic acid will form films with an inherentviscosity of 0.4 dl/g but a suitable elongation at break value is onlyreached with the novel polyesters of the invention having an inherentviscosity of at least 0.1 dl/g, preferably more than 1.2 dl/g. Thepolyesters with an inherent viscosity of 1.0 to 1.5 dl/g can have anelongation at break of about 20% or more and in the inherent viscosityrange of 1.5 to 2.0 dl/g, the elongation at break will be even higher.

In the polyesters of the invention, the inherent viscosity of thepolyesters is greatly dependent upon the purity of the monomer and evenrelatively small variations in the purity of the diphenol monomer cancause large deviations in the inherent viscosity values. The elongationat break values with polyesters of an inherent viscosity of 1.5 to 2.5dl/g, preferably 1.8 to 2.4 dl/g do not appear to change as rapidly withan increase in inherent viscosity as they do at lower inherentviscosities. The result is that elongation at break values can be moreconsistent under actual production conditions.

Polyesters with an inherent viscosity of more than 2.5 dl/g are usuallyonly obtained with a diphenol of extremely high purity so as to beimpractical and those polyesters are not sufficiently soluble inchlorinated organic solvents to obtain film casting solutions of thedesired optimum viscosity.

The polyester films of the invention also have a higher limiting oxygenindex measured by ASTM D 2863-77 than the prior art polyesters with alower inherent viscosity. Polymers with a high oxygen index are becomingmore important, especially in uses when smoke formation and the toxicityof the decomposition products due to thermal decomposition of thepolymer, especially due to fire, can not be tolerated. The polyesters ofthe invention have a very high degree of thermal stability which is adesirable property for electrical insulation purposes.

The polyesters of the invention may contain small amounts, i.e. up to10% by weight, preferably 5 to 8% by weight, of another organicdiphenolic compound such as those of the formula ##STR5## wherein R isselected from the group consisting of alkyl, acyl, cycloalkyl, aryl andhalogenated methylene or other hydrocarbon group as described in U.S.Pat. No. 3,216,970.

The polyesters of the invention may also contain small amounts, i.e. upto 10%, preferably 5 to 8% by weight, of cross-linking agents such as1,2-divinylbenzene, 1,4-divinylbenzene, 1,3-divinylbenzene,1,1,1-trimethylolpropane trimethacrylate and the bismaleimide of4,4'-diaminodiphenylmethane of the formula ##STR6## or3,3'-diallyl-bisphenol A or terephthalic acid substituted in orthoposition with --CH₂ --CH═CH₂ or --COOCH₂ --CH═CH₂.

The coated electrical conductors of the invention are comprised of anelectrical conductor provided with an electrically insulating layer of apolyester of the invention having an inherent viscosity of at least 1.0dl/g and an elongation at break of at least 20%. The layer may beapplied in any suitable manner such as by wrapping the electricalconductor, preferably if it is in wire form, with a film or an adhesivetape, especially a pressure sensitive tape, of the polyester or byplacing a heated conductor in a fluidized bed of polyester powder or anyother known means such as by extrusion or hot melt techniques.

At least some of the polyesters of the invention also have aninteresting bimodal distribution which indicates that the polyesters notonly contain high molecular weight components but also a minor amount ofe.g. 10 to 20% of a low molecular weight component which may increasethe adhesive qualities of the polyesters making them even more useful inthe electrical insulation field.

In the following examples there are described several preferredembodiments to illustrate the invention. However, it should beunderstood that the invention is not intended to be limited to thespecific embodiments.

EXAMPLE 1

871 g (3.0 moles) of 1,1-bis-(4-hydroxyphenyl)-1-phenyl-ethane meltingat 189°-191° C. were dissolved at 70° C. in a solution of 264 g ofsodium hydroxide, 2.0 liters of isopropanol and 4 liters of distilledwater and after cooling the mixture to room temperature, 8 liters ofwater were added to the solution of the disodium phenolate.

The resulting solution was added to a coolable reaction vessel providedwith a high speed stirrer, thermometer and a metering pump followed bythe addition of 15 liters of distilled 1,2-dichloroethane and a roomtemperature solution of 34.5 g (0.15 moles) of benzyl triethylammoniumchloride in 200 ml of distilled water. The mixture was vigorouslystirred while adding over 25 minutes a solution of 304.5 g (1.5 moles)of isophthaloyl chloride and 304.5 g (1.5 moles) of terephthaloylchloride in 2.0 liters of 1,2-dichloroethane which had been stored underanhydrous conditions while keeping the temperature below 40° C. Themixture was stirred for 45 minutes during which the viscosity increased.

The resulting mixture was allowed to stand for 15 minutes to form anaqueous phase which was discarded and an highly viscous organic phase.The latter was washed three times with 30 liters of water each time andwas then vigorously stirred with 30 liters of isopropanol after whichthe desired polyester precipitated. The mixture was filtered and thepolyester product was admixed with an additional 30 liters ofisopropanol. The mixture was centrifuged and the recovered product waswashed twice with 10 liters of water each time to remove residualinorganic salts. The resulting polyester product was dried in acirculating air oven at 130° C. for 15 hours to obtain a constant weightproduct of 1,197 g (95% yield) of the polyester. The inherent viscositywas determined to be 2.0 dl/g using a solution of 0.5 g of the polyesterin 100 ml of a mixture of 60% by weight of phenol and 40% by weight of1,1,2,2-tetrachloroethane and a Ubbelohde viscometer at 30° C.(capillary constant--0.01).

EXAMPLE 2

The procedure of Example 1 was repeated using 2.0 liters of ethanol inplace of isopropanol to obtain 1,210 g (96% yield) of the polyesterhaving an inherent viscosity of 1.65 dl/g.

EXAMPLE 3

A solution of 7.5% by weight of the polyester of Example 1 in1,2-dichloroethane was used as a coating solution in a film castingmachine to form a film of the polyester with a thickness of 0.025 mm.The elongation at break of the film was determined by ASTM D 882-75 b tobe 61%. Another film of the polyester of Example 1 with a thickness of0.125 mm was prepared from the same casting solution and the oxygenindex of the film was determined by ASTM D 2683-77 to be 27%.

EXAMPLE 4

Using the procedure of Example 1, 2 moles of1,1-bis-(4-hydroxyphenyl)-1-phenyl-ethane with a melting range of189°-191° C. and 2 moles of terephthaloyl chloride were reacted in thepresence of isopropanol with benzyltriethylammonium chloride as catalystfor 45 minutes to obtain a polyester with an inherent viscosity of 2.23dl/g. The cast films of the said polyester had an elongation at break of46% by the ASTM test of Example 3.

EXAMPLE 5

Using the procedure of Example 1, 2 moles of1,1-bis-(4-hydroxyphenyl)-1-phenyl-ethane and 2 moles of an equimolarmixture of terephthaloyl chloride and isophthaloyl chloride in thepresence of isopropanol with benzyl triethylammonium chloride ascatalyst were reacted for 45 minutes to obtain a polyester with aninherent viscosity of 2.11 dl/g. The cast films of the said polyesterhad an elongation at break of 41% using the ASTM test of Example 3.

EXAMPLE 6

Using the procedure of Example 1, 2 moles of1,1-bis-(4-hydroxyphenyl)-1-phenyl-ethane and 2 moles of isophthaloylchloride were reacted in the presence of isopropanol with benzyltriethylammonium chloride as catalyst to form a polyester with aninherent viscosity of 1.21 dl/g. The cast film of the said polyester hadan elongation at break of 44% with the ASTM test of Example 3.

EXAMPLE 7

To demonstrate the advantageous properties obtained by the use of a morepure monomer, 2 moles of 1,1-bis-(4-hydroxyphenyl)-1-phenyl-ethane witha melting range of 183°-189° C. (product A), 185°-190° C. (product B)and 188°-190° C. (product C) and 2 moles of an equimolar mixture ofisophthaloyl chloride and terephthaloyl chloride were reacted in thepresence of isopropanol with benzyltriethylammonium chloride as catalystto obtain the corresponding polyesters whose inherent viscosity andelongation at break are reported in Table I.

                  TABLE I                                                         ______________________________________                                                       Inherent viscosity                                                                         % elongation                                      Polyester of monomer                                                                         dl/g         at break                                          ______________________________________                                        A              0.99         16                                                B              1.65         32                                                C              2.11         47                                                ______________________________________                                    

The results of Table I clearly show that the more pure the startingdiphenol monomer, the better properties of the resulting polyester asindicated by the higher inherent viscosity and percentage of elongationat break.

EXAMPLE 8

In order to demonstrate the advantageous properties of the polyesters ofthe invention, the films of the above examples were subjected to aseries of tests and the results are reported in the following Table. Thedielectric constant and dielectric factor was determined by DIN 53483and the dielectric strength which is an important measured value wasdetermined in volts per mil. The elongation at break and tensilestrength were determined by DIN 53455 and the elastic modulus wasdetermined by DIN 53457. The gel permeation chromatogramm was alsodetermined together with a thermogravimetric analysis. The punctureresistance and high temperature film shrinkage and film weight loss weredetermined as well as the degree of water absorption.

                                      TABLE                                       __________________________________________________________________________                                             Thermo-                                                                       gravimetric                          Dielectric Dissipation                                                                         Dielectric    Tensile                                                                            Elastic                                                                            analysis 0° C.                                                                   Puncture                                                                            Penetra-             Film of                                                                            constant                                                                            factor                                                                              strength in                                                                         % elongation                                                                          strength                                                                           modulus                                                                            5%   20%  Resistance                                                                          tion                 example                                                                            at 1.0 KHz                                                                          at 1.0 KHz                                                                          volt/mil                                                                            at break - max.                                                                       K psi                                                                              K Psi                                                                              loss in N.sub.2                                                                    loss in N.sub.2                                                                    in lbs/mil                                                                          temp.                __________________________________________________________________________                                                             °F.           7A   3.0   .005  --    16      10.9 204  482° C.                                                                     510° C.                                                                     3.1   553                  7B   3.1   .005  4174  32      10.6 203  485° C.                                                                     515° C.                                                                     3.3   567.5                7C   --    --    4349  47      9.3  207  484° C.                                                                     510° C.                                                                     4.3   525                  __________________________________________________________________________

    ______________________________________                                        % Film Shrinkage                                                                            Water absorption                                                                           % weight loss                                      after 15 min. % change in  at 220° C. for                              at 200° C.                                                                           weight       24 hours                                           ______________________________________                                        0.49          +.33         -1.7                                               0.59          +.35         -.77                                               1.48          +0.51        -4.6                                               ______________________________________                                    

What we claim is:
 1. An electrical conductor provided with anelectrically insulating layer of an organic, high-molecular weightpolyester containing substantially chain members of the formula ##STR7##wherein X is at least one member selected from the group consisting of##STR8## having an inherent viscosity of at least 1.0 dl/g measured at30° C. in a solution of 0.5 g of the polyester in 100 ml of a mixture of60% by weight of phenol and 40% by weight of 1,1,2,2-tetrachloroethaneand whose films cast from a chlorinated organic solution have anelongation at break of more than about 20%.
 2. An conductor of claim 1wherein the inherent viscosity of the polyester is at least 1.2 dl/g. 3.A conductor of claim 1 wherein the elongation at break of the polyesteris at least 40%.
 4. A conductor of claim 1 wherein X is the polyestermixture of 70 to 30% by weight of ##STR9##
 5. A conductor of claim 4wherein the mixture is a 50% to 50%.
 6. A conductor of claim 1 whereinthe inherent viscosity of the polyester is greater than 1.5 dl/g.
 7. Aconductor of claim 1 wherein the inherent viscosity of the polyester isgreater than 1.8 dl/g.
 8. A method of insulating an electrical conductorcomprising providing the exterior surface of the electrical conductorwith an electrically insulating layer of an organic, high-molecularweight polyester containing substantially chain members of the formula##STR10## wherein X is at least one member selected from the groupconsisting of ##STR11## having an inherent viscosity of at least 1.0dl/g measured at 30° C. in a solution of 0.5 g of the polyester in 100ml of a mixture of 60% by weight of phenol and 40% by weight of1,1,2,2-tetrachloroethane and whose films cast from a chlorinatedorganic solution have an elongation at break of more than about 20%. 9.The method of claim 8 wherein the inherent viscosity of the polyester isat least 1.2 dl/g.
 10. The method of claim 8 wherein the elongation atbreak of the polyester is at least 40%.
 11. The method of claim 8wherein X is a mixture of 70 to 30% by weight of ##STR12##
 12. Themethod of claim 11 wherein the mixture is a 50% to 50%.
 13. The methodof claim 8 wherein the inherent viscosity of the polyester is greaterthan 1.5 dl/g.
 14. The method of claim 8 wherein the inherent viscosityof the polyester is greater than 1.8 dl/g.